sea spider

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sea spider,

common name for members of the class Pycnogonida, long-legged, rather spiderlike organisms of the subphylum Chelicerata, widely distributed in marine waters. Most are tiny, from 1 to 9 mm (0.04–0.36 in.), and live in littoral regions, crawling about over the surface of sessile animal colonies or seaweeds. Some live on or in clams. There are deep-sea forms, some becoming quite large; Colossendeis colossea has a leg span of nearly 2 ft (91 cm). Their unusual body form makes their relationships to other arthropods obscure. Nearly all of the body is composed of the anterior region (prosoma); a tiny tubular posterior region (opisthosoma) projects behind. A large proboscis is used to suck in food. At the base of the proboscis is a pair of modified appendages (chelicera) used to pick off bits of food and hold them in front of the mouth. The next appendages are a pair of leglike pedipalps, followed by a pair of specialized legs used by the male to carry eggs until they hatch. Four to six pairs of walking legs follow. The reduced body size has led to the extension of the organs into the appendages. They lack gills or lungs; oxygen is absorbed from seawater through diffusion, using pores in the exoskeleton in the largest sea spideers. Members of this class are relatively common and widely distributed; some 1,300 species are known. Sea spiders are classified in the phylum ArthropodaArthropoda
[Gr.,=jointed feet], largest and most diverse animal phylum. The arthropods include crustaceans, insects, centipedes, millipedes, spiders, scorpions, and the extinct trilobites.
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, subphylum ChelicerataChelicerata
, subphylum of Arthropoda, including the horseshoe crabs (order Xiphosura), the arachnids (class Arachnida), and the sea spiders (class Pycnogonida). The extinct giant water scorpions (order Eurypterida, not true scorpions) also are chelicerates.
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, class Pycnogonida.

sea spider

[′sē ‚spī·dər]
(invertebrate zoology)
The common name for arthropods in the subphylum Pycnogonida.
References in periodicals archive ?
We tested the effect of cuticular waxes on epibiont cover by cutting each of 16 pycnogonids longitudinally down the center of its trunk and separating the halves into two groups: an experimental group, in which waxes were removed, and a control group, in which the waxes were left intact.
Change in percent epibiont cover did not vary significantly with experimental (restricted ovigers) and control (unrestricted ovigers) pycnogonids (Z = 37, d.f.
In bright light, epibionts on pycnogonids produced high levels of oxygen locally.
We collected some pycnogonids at depths of 20-30 m and on the undersides of submerged concrete blocks--sites that likely received very little light and would support very low levels of photosynthesis.
Several species of pycnogonids have been reported to use their ovigers to groom their cuticles (King, 1973; Arnaud and Bamber, 1987; Davenport et al., 1987; Bamber, 2007).
There was some evidence that waxes (or chemicals present in those waxes; see Fahrenbach, 1994, and Melzer et al., 1996) on pycnogonids prevent epibiont attachment (Fig.
Using two species of temperate pycnogonids, we have shown that macroepibionts do not restrict local oxygen availability, and, in some cases, they may raise local oxygen levels.
Future studies should also determine whether pycnogonids structure their cuticles to recruit epibionts--for camouflage or to control infections (Armstrong et al., 2000; Dougherty and Russell, 2005).
We measured oxygen levels in the bulk seawater 1 cm from the pycnogonid, and at the surface of the cuticle of individuals with or without heavy epibiont coverage (n = 8 per group).
However, one pycnogonid from the experimental group lost a single oviger.
Individual patches of epibionts were outlined, summed, and divided by the total area of the pycnogonid (Chung et al., 2007).